My :twocents: :

The cephalopod eye is a miracle of engineering, and its a design that shows convergent evolution at its finest.

The general vertebrate eye (let's use our own for example) :cyclops: has a set of cells; they are rods and cones. Light enters the eye, passes through a layer of glial cells, and hits said rods and cones thus producing the signal that is read by our brain as "sight". (mind you, I'm really oversimplifying this due to the fact that I tend to get over-scientific at times :oops: )

The ceph eye has no rods nor cones. What they do have are photoreceptors (light-gathering cells) called rhabdomeres, which pretty much take the place of our rods and cones. Light passes directly through the lens and is collected by these photoreceptors. The pigments in these structures move with the light, and the lens is actually controlled by muscles, drawn in or out to focus on objects at various distances. So, no, they cannot "see" color, but can discern various shades of light intensity and therefore can probably percieve what we consider mere black and white into much more.

A lot also has to do with the number of cells per square millimeter of retinal tissue, and the fact that the cephalopod brain has a huge section of resources dedicated to optics and sight.

So they don't see true "color", but they pretty much discern it. At least, that's the way I see it.

Thankyou for spelling that out in black and white for us, John. Very interesting.

Okay, here comes some more science, folks! :grad: Sorry...

Something occured to me today, thanks to my physiology instructor... An interesting sidenote to the concepts about the eye has yet to be mentioned - selective pressure and its effects on form and function.

Our eyes use the aforementioned glial cells to process the sensory information early (before the rods and cones get hit by light). This way, they do a lot of the work saving the brain some energy (and work). I wonder if this is partially how hallucinations work? But I digress...

The ceph eye has no pre-processing, so the light goes right to the rhabdomeres, right? Animals on land that depend heavily on light-gathering eyes (nocturnals mostly), usually have less color vision or see in "black and white". I think this may be due to the tapetum lucidum (the silvery film that reflects light in vertebrates - think how cats eyes seem to "glow") and that night vision tends to sacrifice color for view.

Where do cephs live? Water pretty much blows when it comes to conducting light as well as air. The photic zone is what... about 100 meters or so? Cephs need light resolution far more than color vision, and also, color tends to get warped in the water. If you have eyes like a vertebrate, you'll have the same visual weaknesses as a vertebrate. Form follows function.

What I was wondering was if the retina of the ceph reflects light like a tapetum lucidum?

In short, I think its all a matter of selective pressure on the eyes.

Sushi and Salmon Roe, and raspberry sake


"Pulling out jives and jamboree handouts, two turntables and a microphone..." - Beck
I was going to say all that about the rods and cones lark! How rude!

Something did strike me though:

If you squint, you change your intake of focal light, and compress it to hit more on the colour receptors of the back of your eye...if you widen your eyes, you gain a better black/white/movement vision

Could an Octo do this too? Could they squint to alter their perception of things?

Anyway I am pretty badly scuppered when it comes to colour vision, red/green/brown... blue/purple

Not too good eh. Out of that CB page I could only see the first one and in the last couldn't make out jack. I think I might add a few more arms to me and become an octo... they have it easy!

But yeah, they shouldn't need colour vision, if you do only see in shades of grey then you could just belnd to the same shade... clever eh!


Actually, the ceph eye moves its lens in and out from the retina, by way of ciliary muscle action. Its like the lens on an SLR camera. This is a magnificient design.

Yet another sidenote in the natural history of the cephalopod eye: Our eyes use a strange system of processing, whereas rods and cones point backward to catch reflecting light. Ceph eyes dierctly catch the light by pointing forwards. And the reason I find this interesting is that the eyes develop within invaginations (in-pockets of the skin) similar to the pigment-cup ocelli of flatworms and such. Vertebrate eyes have developed as a part of the brain. Its also believed that they see polarized light, so color perception isn't quiet as important as light perception.

Yeah, they are a magnificent design.

What I know is that the *^%#^&#^ so and so's can adjust for refraction at the water's surface! I managed to annoy Delphine this morning and from under the water I got doused .......Her aim was spot on too!


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